306 TECTONIC GEOLOGY 



As already stated, the rocks of the great horst of Antarctica have not up to the 

 present shown evidence of any marked folds, but are rather of the plateau type, with 

 large broken segments characteristic of the Atlantic variety of coast-line. 



Dr. P. Marshall,* in an able address to the Australasian Association for the 

 Advancement of Science at Brisbane in 1910, has pointed out that in his opinion too 

 much stress has been laid on these so-called Atlantic and Pacific types of petro- 

 graphical provinces. He notices the importance and continuity of the Tonga 

 Kermadec Deep, and in his map makes it clear that in his opinion the ocean deep 

 to the east of the Chatham Islands is prolonged in a south by west direction 

 parallel to the Tongan Kermadec Deep down towards Ross Sea. He states 

 (oj). cit., p. 448): — 



" The New Zealand coasts are not determined by fault planes, but their main 

 directions are at least as old as the Miocene period. The main period of mountain 

 formation in New Zealand was in the late Jurassic, and was possibly contem- 

 poraneous with rock folding in New Caledonia, but preceded the movement in the 

 New Hebrides," " Much of the New Zealand coast-line is of the Atlantic type." 

 " The occurrence of alkaline rocks in mid-Pacific goes far to negative the idea that 

 alkaline eruptives are associated with the occurrence of the Atlantic coast type." 

 In reference to this last statement, we may point out that Dr. Harker (oj:*. cit., p. 98) 

 has already commented on this point and sought to explain it. He states " the 

 case of the Galapagos Group, however, is instructive. These islands, situated some 

 800 miles west of the Andes, nevertheless have volcanic rocks of distinctly Atlantic 

 phases." Now Suess makes this group of volcanoes a critical point in his syntaxis 

 of the American mountain chains, and notes that it presents " the same formation 

 and association as occurs elsewhere in the Atlantic region." In another place he 

 says, " Wolfe rightly places these islands among the group volcanoes as opposed to 

 the serial volcanoes of the mainland, and emphasizes the petrological contrast between 

 them and the volcanoes of Ecuador. Here we see how the tectonic type character- 

 istic of the Atlantic is associated with rocks of what we have styled Atlantic phases, 

 even when it appears exceptional within the Pacific territory." 



Marshall emphasizes the fact that there are many exceptions besides the Gala- 

 pagos to the rule of the Pacific rock types existing within the Pacific area. 

 Trachytes f occur at the Auckland and Campbell Islands of the Sub-Antarctic, as 

 well as at Dunedin. Trachytes, bostonites, and phonolites rich in nepheline occur 

 near Dunedin. 



Basanites occur at Auckland, where they are widely distributed. Kleinschmidt 



* Ocean Contours ami Earth Movements in the South-west Pacific, by Dr. P. Marshall, M.A., U.Sc, 

 F.G.S., Professor of Geology, Otago University, New Zealand, Kept. Aus. Assoc. Adv. Science, Brisbane, 

 1910, pp. 447-448. 



t The Sub-Antarctic Islands of New Zealand, Article XXIX. The Geology of Campbell Island 

 and the Snares, Wellington, N.Z. Gov. Printer, 1909. In this paper Marshall describes porphyries 

 with oligoclase surrounded by anorthoclase, trachytes allied to pantellarites, and phonolites. 



